As an example of a passage control device, there is an intake vortex flow generator for an internal combustion engine. The intake vortex flow generator generates an intake vortex flow in the combustion chambers of the internal combustion engine by reducing the sectional areas of intake passages through which intake air flows.
For example, Japanese Unexamined Patent Application Publication No. 2007-085191 describes an intake vortex flow generator designed for improving the combustion efficiency by generating an intake vortex flow such as a swirling flow or a tumbling flow of the mixture in the combustion chambers of the internal combustion engine.
The intake vortex flow generator includes an intake manifold (casing) that connects to intake ports of the internal combustion engine, valve units held in the intake manifold, and a shaft supporting valves of the valve units and driven by an actuator.
Referring to FIGS. 4A and 4B, each valve unit includes a tubular housing 101 held in the intake manifold and a valve 103 disposed in the housing 101. The housing 101 has a rectangular cross-section and forms an intake passage 102 therein. The valve 103 is held in the housing 101 to open and close the intake passage 102. The valve 103 includes a vale body part and a cylindrical valve shaft part 104. The valve shaft part 104 is integrally formed with the valve body part of the valve 103.
In order to smoothly operate the valve 103 in the housing 101, that is, in order to restrict interference between the housing 101 and the valve 103, predetermined gaps must be provided between inner surfaces of the housing 101, which forms the intake passage 102, and the upper and lower, and right and left edge surfaces of the valve 103.
Further, both axial ends of the valve shaft part 104 are rotatably held inside of through holes of the housing 101. The valve shaft part 104 has a through hole therein for allowing a shaft to pass through. Particularly, the valve shaft part 104 includes a square fitting hole 105 in which the shaft will be press-fitted near the central portion of the through hole, as well as circular insertion holes 111 and 112 having a diameter larger than the outer diameter of the shaft on opposite sides of the fitting hole 105.
The shaft has a fitting portion 106 having a polygonal shape in a cross section defined perpendicular to a longitudinal axis of the shaft. The fitting portion 106 is fitted in the fitting hole 105 by press-inserting or press-fitting.
In such a configuration, the fitting portion 106 of the shaft is press-fitted and fixed to the wall surfaces of the fitting hole 105. Here, the fitting hole 105 has the inner diameter smaller than the outer diameter of the fitting portion 106 of the shaft, and is formed over the whole width of the valve body part of the valve 103. Therefore, a press-fitting load at the time of inserting the shaft in a pressed manner is large. Thus, the valve body part, the valve shaft part 104 or the fitting portion 106 of the shaft will be unexpectedly deformed at the time of inserting the shaft in a pressed manner.
For example, it can be contrived to shorten the length of a fitting part between the fitting hole 105 of the valve shaft part 104 and the fitting portion 106 of the shaft in an attempt to decrease the press-fitting load at the time of press-fitting the shaft. In such a configuration, however, there is a probability in that the shaft may be press-fitted in the wall surfaces of the fitting hole 105 in a state where the longitudinal axis of the shaft is tilted relative to a longitudinal axis of the through hole of the valve shaft part 104.
If the shaft is tilted relative to the longitudinal axis of the fitting hole 105, the gap is not properly formed between the housing 101 and the valve 103. Therefore, interference will occur between the housing 101 and the valve 103, causing malfunction of the valve 103 such as locking of the valve 103.